Southern central Australia, including the Eyre pen

Extending off southern Australia, the Eyre and Yorke Peninsulas are characterized by complex geology, morphologically similar vegetation, and a recent history of extensive clearing. The temperate climate and relatively productive soils in this region mean that native vegetation has been severely reduced. Local extinctions and reductions in bird and mammal populations have resulted. Although clearing has declined, the region’s biodiversity is threatened by fragmentation, alien species, and alterations in fire regimes.

Scientific Code

(AA1203)

Ecoregion Category

Australasia

Size

23,500 square miles

Status

Critical/Endangered

Habitats

Description Location and General DescriptionThis ecoregion encompasses areas of extensive mallee vegetation geographically isolated from the Murray-Darling Woodlands and Mallee ecoregion to the east, and from similar formations in Western Australia. The ecoregion includes two peninsulas (Eyre to the west and Yorke to the east), separated by the Spencer Gulf. Both are characterized by a complex geological history, and the exposed substrate is a mix of old metamorphic rocks, granite outcrops, consolidated limestones, and more recent sediments, including siliceous sands (Parker et al.1985). The rainfall in the areas ranges from 600 mm in the south to 350 mm in the north of Eyre Peninsula, predominantly falling in winter. This variation in rainfall together with the geological heterogeneity results in a variety of environments, and the consequent high diversity of the region (Schwerdtfeger 1985).

Both the Eyre and Yorke Peninsulas were once covered with dryland teatree (Melaleuca lanceolata) woodlands with herbaceous understories. Vegetation in this ecoregion has been extensively cleared for agriculture and development. Dryland teatree and mallee box (Eucalyptus porosa) communities were once widespread on Yorke Peninsula. Mallee box is also found on Eyre Peninsula. On western Eyre Peninsula, mallee box grew in association with dryland teatree and southern native pine (Callitris preissii). Other species present include Acacia ligulata, Geijera linearifolia, and E. diversifolia, with Stipa eremophila and Danthonia caespitosa as the main grasses. Other eucalypt woodlands are dominated by sugar gum (E. cladocalyx), river red gum (E. camaldulensis), peppermint box (E. odorata), or the endemic Eyre Peninsula blue gum (E. petiolaris) (Paton et al. 1999).

Biodiversity FeaturesIn spite of the structural homogeneity of the vegetation, biogeographically the two peninsulas that form this ecoregion are quite different. While Eyre Peninsula has strong affinities to the Western Australia biota, in particular from the floristic point of view (Spech 1972), Yorke Peninsula’s biological affinities lean strongly towards southeastern Australia (Specht 1972). Eyre Peninsula is a local center of plant species endemism, with 29 endemic species mostly concentrated towards the southern end of the Peninsula (Davies 1982). Another substantial number of species are found as disjunct populations (mostly from locations in Western Australia).

The isolation of this region from other areas with similar environments, and the diversity of substrates have favored the formation of some unique types of vegetation. Granite outcrops, in particular exhibit remarkable diversity. As with the flora, the avifauna have strong affinities to the Western Australian avifauna, although the eastern influence is noticeable in Yorke Peninsula. The high diversity of environments in Eyre Peninsula is probably the reason for a diverse herpetofauna, particularly the Agamid and Scincidae families (dragon and skink lizards respectively) (Cogger 2000).

As in many other heavily altered habitats, a large proportion of the medium sized marsupials have become locally extinct, or declined substantially. Several are now restricted to offshore islands. Mammals that have been extirpated from southern Eyre Peninsula include tammar wallaby (Macropus eugenii), southern brown bandicoot (Isoodon obesulus), the vulnerable greater bilby (Macrotis lagotis), the endangered western barred bandicoot (Perameles bougainville), the vulnerable burrowing bettong (Bettongia leseur), and brush-tailed bettong (Bettongia pencillata) (Hilton-Taylor 2000, Paton et al. 1999). Bird populations have suffered similar local declines and extinctions (Paton et al. 1999, Stattersfield et al. 1998).

The scattered salt lakes constitute peculiar environments. They are subject to seasonal fluctuations in salinity, and often dry out completely. Although relatively species poor, they contain assemblages of invertebrates that are unique to these environments (Williams 1987). The bottom of these lakes are covered by algal mats. In a few lakes, these mats form stromatolites, similar to the oldest known fossils.

Current Status Most areas suitable for agriculture have been extensively cleared, and there are large tracts of land where native vegetation is mainly found as small remnants, or linear corridors along roads. The process has been more thorough in Yorke Peninsula, partly because of its higher agricultural potential, and partly because of historical reasons (Meining 1962). Because of its marginal productivity the northern part of Eyre Peninsula has not suffered the same degree of clearance, and many large portions of the landscape are still covered by mallee vegetation. Several large conservation areas have also been set aside across Eyre Peninsula. In Yorke Peninsula, Innes National Park stands out as the only large piece of intact vegetation. Coastal vegetation, however, is overall better preserved, in particular that on limestone or sand dunes. Overall, around 7 percent of the plant taxa have become extinct, while almost 50 percent of the plant species listed for the region have conservation significance (Lang and Kraehenbuehl 1987).

Types and Severity of ThreatsWhile the rate of vegetation clearance has abated, small remnants are threatened by encroachment, weed infestation, and, in some cases, agricultural runoff. On Eyre Peninsula, tree decline is caused by rising saline groundwater, flooding due to increased surface runoff, and lowering of the water table. Changes in fire regimes may pose a threat for some species and communities. While the northern fringe of the region in the Eyre Peninsula largely retains its integrity, changes in agricultural technology may impact this region. Fragmentation poses a serious threat to native fauna, and introduced mammals such as cats (Felis catus), foxes (Vulpes vulpes), and rabbits (Oryctolagus cuniculus) are adversely affecting native biota.

Justification of Ecoregion DelineationThe Eyre and Yorke Mallee ecoregion comprises one IBRA, the ‘Eyre and Yorke Blocks’ (Thackway and Cresswell 1995). The Yorke Peninsula and the western edge of the Eyre Peninsula comprise the western limit of the ‘South-east Australia’ Endemic Bird Area (Stattersfield et al. 1998). Vegetation originally consisted of mallee woodlands, shrublands, and heath. This region’s mediterranean climate separates it from arid regions to the north.

Thackway, R. and I. D. Cresswell. editors. 1995. An Interim Biogeographic Regionalisation for Australia: a framework for establishing the national system of reserves, Version 4.0. Australian Nature Conservation Agency, Canberra.